A microarray-based analysis of oocyte quality in the European clam Ruditapes decussatus

Abstract

A microarray-based analysis was performed with the objective of describing genomic features of oocytes and looking for potential markers of oocyte quality in the economically important European clam, Ruditapes decussatus. Oocytes of 25 females from Ria de Aveiro, Western coast of Portugal (40°42′N; 08°40′W) were selected for this study and oocyte quality was estimated by success of D-larval rate under controlled conditions, which appeared to vary from 0 to 95 %. By genome-wide expression profiling with a DNA microarray, 526 probes appeared differentially expressed between two groups representing the largest and smallest value of D larval rates, named good (represented by a mean D-larval yield of 57 ± 22%) and poor (9 ± 5%) quality oocytes. Enrichment analysis showed “Lysosome” (dre04142) as the single pathway represented in the enriched KEGG pathway terms, with 8 genes coding for putative Cathepsins. Furthermore, differentially expressed genes involved in oocyte protection (DnaJ (Hsp40), Hsp70, Cyclophilin B, PDI), maturation (Cam-PDE1C, PRDM9, G protein), sperm-egg interaction (PDI, G protein) and apoptosis (TNF) were also identified. From these, the apoptosis pathway was supposed to assume an important role in oocyte quality as the mRNA level of Caspase 8 appeared also negatively correlated with the D-larval yield. Finally, a G-protein transcript was identified as more abundant in poor quality oocytes, which underlines the importance of release prophase I block and meiotic maturation in the oocytes of this species. This study provided new highly valuable information on genes specifically expressed by mature oocytes of R. decussatus, for further understanding of the mechanisms of early development in this species

Transcriptomic features of Pecten maximus oocyte quality and maturation

“… Values of D-larval rates of released oocytes (REL) expressed as percentages of trochophore at 48 hpf on the total count of oocytes employed for the fertilization. Standard deviation refers to batch replicates (n = 3) as described in [ 20 ]. …”

“…This was also suggested in R . decussatus oocytes, showing a negative correlation between D-larval yield and Caspase 8 (CASP8) [ 20 ]. GADD45A is a stress-inducible nuclear protein involved in maintenance of genomic stability, senescence, apoptosis, DNA repair [ 77 ] and suppression of cell growth, and has a key role in active DNA demethylation that occurs in Xenopus oocytes [ 78 ].…”

“…Trochophores movement was estimate at 24h post fertilization using a CASA device, according to [ 35 ]. Then, the D-larval yield was assessed at 48h post fertilization (number of normal D-larvae/total number of oocytes) as described in [ 20 ].…”

“…Some quality criteria are size, shape, transparency, chorion and coelomic fluid aspects, distribution and volume of lipid droplets and floatability rate [ 27 ]. In addition, recent studies demonstrated that transcriptomic and proteomic data might be associated to low or high quality eggs [ 19 – 20 , 28 – 29 ]. However, an effective and simple proxy of gamete quality does not exist yet and it is still very difficult to accurately assess the quality of gametes prior to fertilization [ 21 ].…”

Mortality event involving larvae of the carpet shell clam Ruditapes decussatus in a hatchery: isolation of the pathogen Vibrio tubiashii subsp. europaeus

“…The success of D‐larval rate in R. decussatus is highly variable, reflecting the individual differences in oocyte quality, caused by different factors that have not yet been elucidated (de Sousa et al . ). In this case, apart from other factors, a problem related to the presence of the pathogen VTE should be considered.…”